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The yields of [Formula omitted] mesons have been measured in inelastic p+p interactions at incident projectile momenta of 31, 40 and 80 [Formula omitted] ( [Formula omitted] and 12.3 [Formula omitted], respectively). The data were recorded by the NA61 [Formula omitted]SHINE spectrometer at the CERN Super Proton Synchrotron and the [Formula omitted] mesons identified via their decays into [Formula omitted] pairs. Double-differential distributions are presented as function of transverse momentum and rapidity. The mean multiplicities of [Formula omitted] mesons were determined to be [Formula omitted] at 31 [Formula omitted], [Formula omitted] at 40 [Formula omitted] and [Formula omitted] at 80 [Formula omitted]. The results on [Formula omitted] production are compared with the production of charged kaons in corresponding reactions and with model calculations (Epos1.99, SMASH 2.0 and PHSD) as well as with published data from other experiments.

The NA61/SHINE experiment at the CERN Super Proton Synchrotron studies the onset of deconfinement in strongly interacting matter through a beam energy scan of particle production in collisions of nuclei of varied sizes. This paper presents results on inclusive double-differential spectra, transverse momentum and rapidity distributions and mean multiplicities of [Formula omitted], [Formula omitted], p and [Formula omitted] produced in [Formula omitted] collisions at beam momenta of 13A, 19A, 30A, 40A, 75A and 150A [Formula omitted]. The analysis uses the 10% most central collisions, where the observed forward energy defines centrality. The energy dependence of the [Formula omitted]/ [Formula omitted] ratios as well as of inverse slope parameters of the [Formula omitted] transverse mass distributions are placed in between those found in inelastic [Formula omitted] and central Pb + Pb collisions. The results obtained here establish a system-size dependence of hadron production properties that so far cannot be explained either within statistical or dynamical models.

This paper reports measurements of two-pion femtoscopic correlations in Be+Be collisions at a beam momentum of 150 [Formula omitted] (energy available in the center-of-mass system for nucleon pair [Formula omitted] GeV) by the NA61/SHINE experiment at the CERN SPS accelerator. The obtained momentum space correlation functions can be well described by a Lévy distributed source model. The transverse mass dependence of the Lévy source parameters is presented, and their possible theoretical interpretations are discussed. The results show that the Lévy exponent [Formula omitted] is approximately constant as a function of [Formula omitted], and far from both the Gaussian case of [Formula omitted] or the conjectured value at the critical endpoint, [Formula omitted]. The radius scale parameter R shows a slight decrease in [Formula omitted], which can be explained as a signature of transverse flow. Finally, an approximately constant trend of the intercept parameter [Formula omitted] as a function of [Formula omitted] was observed, similar to previous NA44 S + Pb results (obtained with a Gaussian approximation, but unlike RHIC results).

The critical point of dense, strongly interacting matter is searched for at the CERN SPS in .sup.40Ar + .sup.45Sc collisions at 150A Ge V /c. The dependence of second-order scaled factorial moments of proton multiplicity distribution on the number of subdivisions of transverse momentum space is measured. The intermittency analysis is performed using both transverse momentum and cumulative transverse momentum. For the first time, statistically independent data sets are used for each subdivision number. The obtained results do not indicate any statistically significant intermittency pattern. An upper limit on the fraction of correlated proton pairs and the power of the correlation function is obtained based on a comparison with the Power-law Model developed for this purpose.

The NA61/SHINE collaboration studies at the CERN Super Proton Synchrotron (SPS) the onset of deconfinement in hadronic matter by the measurement of particle production in collisions of nuclei with various sizes at a set of energies covering the SPS energy range. This paper presents results on inclusive double-differential spectra and mean multiplicities of [Formula omitted] mesons produced in the 5% most central [Formula omitted]Be + [Formula omitted]Be collisions at beam momenta of 19A, 30A, 40A, 75A and 150 [Formula omitted] obtained by the so-called [Formula omitted] method which does not require any particle identification. The shape of the transverse mass spectra differs from the shapes measured in central Pb + Pb collisions and inelastic p+p interactions. The normalized width of the rapidity distribution decreases with increasing collision energy and is in between the results for inelastic nucleon-nucleon and central Pb + Pb collisions. The mean multiplicity of pions per wounded nucleon in central [Formula omitted]Be + [Formula omitted]Be collisions is close to that in central Pb + Pb collisions up to 75 [Formula omitted]. However, at the top SPS energy the result lies between those for nucleon-nucleon and Pb + Pb interactions. The results are discussed in the context of predictions for the onset of deconfinement at the CERN SPS collision energies.

This paper presents results on multiplicity fluctuations of positively and negatively charged hadrons as well as net-electric charge fluctuations measured in central Ar+Sc interactions at beam momenta 13A, 19A, 30A, 40A, 75A, and 150 A GeV/c. The fluctuation analysis is one of the tools to search for the predicted critical point of strongly interacting matter. Results are corrected for the experimental biases and quantified using cumulant ratios. In most instances, multiplicity and net-charge distributions appear narrower than the corresponding Poisson or Skellam distributions. Cumulant ratios are compared with the EPOS1.99 model predictions, which provide a qualitative description that aligns with observations for positively and negatively charged particles. The obtained results are also compared to earlier NA61/SHINE results from inelastic p+p interactions in the same analysis acceptance.

The NA61/SHINE experiment at the CERN Super Proton Synchrotron studies the onset of deconfinement in strongly interacting matter through a beam energy scan of particle production in collisions of nuclei of varied sizes. This paper presents results on inclusive double-differential spectra, transverse momentum and rapidity distributions and mean multiplicities of$$\\pi ^\\pm $$π ± ,$$K^\\pm $$K ± , p and$$\\bar{p}$$p ¯ produced in$$^{40}\\hbox {Ar+}^{45}\\hbox {Sc}$$40 Ar+ 45 Sc collisions at beam momenta of 13 A , 19 A , 30 A , 40 A , 75 A and 150 A  $$\\text{ Ge }\\hspace{-1.00006pt}\\text{ V }\\!/\\!c$$Ge V / c . The analysis uses the 10% most central collisions, where the observed forward energy defines centrality. The energy dependence of the$$K^\\pm $$K ± /$$\\pi ^\\pm $$π ± ratios as well as of inverse slope parameters of the$$K^\\pm $$K ± transverse mass distributions are placed in between those found in inelastic$$p+p$$p + p and central Pb + Pb collisions. The results obtained here establish a system-size dependence of hadron production properties that so far cannot be explained either within statistical or dynamical models.

The NA61/SHINE experiment at the CERN Super Proton Synchrotron studies the onset of deconfinement in strongly interacting matter through a beam energy scan of particle production in collisions of nuclei of varied sizes. This paper presents results on inclusive double-differential spectra, transverse momentum and rapidity distributions and mean multiplicities ofπ^(±) ,K^(±) ,pandp̄produced in⁴⁰ Ar+ ⁴⁵ Sc collisions at beam momenta of 13 A , 19 A , 30 A , 40 A , 75 Aand 150 AGeV/ c . The analysis uses the 10% most central collisions, where the observed forward energy defines centrality. The energy dependence of theK^(±) / π^(±)ratios as well as of inverse slope parameters of theK^(±)transverse mass distributions are placed in between those found in inelasticp + pand central Pb+Pb collisions. The results obtained here establish a system-size dependence of hadron production properties that so far cannot be explained either within statistical (SMES, HRG) or dynamical (EPOS, UrQMD, PHSD, SMASH) models.

This paper reports measurements of two-pion femtoscopic correlations in Be+Be collisions at a beam momentum of 150$$A\\,\\hbox {GeV}\\!/\\!c$$A GeV / c  (energy available in the center-of-mass system for nucleon pair$$\\sqrt{s_{\\text {NN}}} = 16.84$$s NN = 16.84 GeV) by the NA61/SHINE experiment at the CERN SPS accelerator. The obtained momentum space correlation functions can be well described by a Lévy distributed source model. The transverse mass dependence of the Lévy source parameters is presented, and their possible theoretical interpretations are discussed. The results show that the Lévy exponent$$\\alpha $$α is approximately constant as a function of$$m_{\\text {T}}$$m T  , and far from both the Gaussian case of$$\\alpha = 2$$α = 2 or the conjectured value at the critical endpoint,$$\\alpha = 0.5$$α = 0.5 . The radius scale parameter R shows a slight decrease in$$m_{\\text {T}}$$m T  , which can be explained as a signature of transverse flow. Finally, an approximately constant trend of the intercept parameter$$\\lambda $$λ as a function of$$m_{\\text {T}}$$m T  was observed, similar to previous NA44 S + Pb results (obtained with a Gaussian approximation, but unlike RHIC results).